Many electronic devices may generate a plurality of signals that need to be transmitted internally or externally. To avoid a high number of signal lines a variety of coding and multiplexing schemes are known in the art. Their applicability depends on the specific technology and, thus, allow more or less reduction in necessary signal wires.
In particular in the field of medical image technology such as Positron Emission Tomography (PET) or gamma cameras, at least one photo detector matrix is used. In a PET scanner, a high number of photomultiplier tubes (PMT) is usually arranged in a circle. To conduct a so-called PET scan, a short-lived radioactive tracer isotope, which decays by emitting a positron, is injected usually into the blood circulation of a living subject. After the metabolically active molecule becomes concentrated in tissues of interest, the research subject or patient is placed in the imaging scanner. The molecule most commonly used for this purpose is fluorodeoxyglucose (FDG), a sugar, for which the waiting period is typically an hour.
As the radioisotope undergoes positron emission decay, it emits a positron, the antimatter counterpart of an electron. After traveling up to a few millimeters the positron encounters and annihilates with an electron, producing a pair of gamma photons moving in almost opposite directions. These are detected when they reach a scintillator material in the scanning device, creating a burst of light which is detected by photomultiplier tubes (PMT) or silicon avalanche photodiodes (Si APD). The technique depends on simultaneous or coincident detection of the pair of photons.
The raw data collected by a PET scanner are a list of ‘coincidence events’ representing near-simultaneous detection of annihilation photons by a pair of detectors. Each coincidence event represents a line in space connecting the two detectors along which the positron emission occurred. Coincidence events can be grouped into projections images, called sinograms. The sinograms are sorted by the angle of each view and tilt, the latter in 3D case images. The sinogram images are analogous to the projections captured by computed tomography (CT) scanners, and can be reconstructed in a similar way.
A PMT can be used in many imaging systems, such as PET scanners and gamma cameras. Each PMT produces one or more signals that need to be processed to generate an image from a plurality of single events that are detected by a PMT. The processing of these signals is performed either internally or these signals are transmitted to an external processing station. In modern PET scanners each PMT may generate a plurality of signals, e.g., a PMT may be able to differentiate as many as 256 different positions and thus would require as many signal wires to identify each specific geometric position within the matrix of scintillator crystals. Thus, a high number of wires is required to transmit these signals.
Thus, there exists a need for an improved multiplexing scheme for transmitting analog digital signals associated with a specific location.